N,N-di(n-lower alkyl)-meta-toluamides are useful as agricultural agents and insecticides. In particular, N,N-diethyl-meta-toluamide is widely used as an active ingredient in insect repellent formulations. Because of its availability and relatively low cost, meta-toluic acid is a highly preferred starting material in the preparation of these compounds. Thus, one known method of preparing N,N-diethyl-m-toluamide is a two-step process in which m-toluic acid and phosphorus oxychloride are reacted in the liquid phase with diethylamine. One disadvantage of this known method is the cost of phosphorus oxychloride and alkali needed to neutralize residual amounts of this reactant after completion of the first step. Another disadvantage is the generation of gaseous hydrogen chloride as a reaction product in the second step of the preparation.
U.S. Pat. Nos. 2,932,665 and 3,198,831 disclose processes for the preparation of N,N-diethyl-toluamides involving the reaction of a toluic acid with diethylamine in the vapor phase in the presence of silica gel, alumina or boron phosphate catalyst. The former of these patents also teaches that liquid phase reaction of m-toluic acid with diethylamine in the presence or absence of a dehydration catalyst to produce N,N-diethyl-m-toluamide is marked by long reaction times plus generation of objectionable amounts of odor and color bodies and undesired by-products, and that the catalyzed and uncatalyzed reaction yields are substantially the same.
U.S. Pat. No. 3,825,596 discloses a liquid phase process for producing N,N-di(lower alkyl)-m(and p)-toluamides in which m(or p)-tolunitrile, a di(lower alkyl) amine and water are contacted at a temperature of 100.degree. C. to 400.degree. C., preferably in the presence of a catalyst selected from the group consisting of inorganic acids, organic acids, organic acid metal salts, metal halides, and peroxides. The preferred organic acid metal salts and metal halides are the acetates and chlorides of copper, zinc, cadmium, mercury, nickel, cobalt and lead. Care must be taken to remove ammonia, a reaction product, from the reaction system in order to obtain a satisfactory reaction yield. U.S. Pat. No. 3,825,596 teaches that the process described therein is not a dehydration reaction.